With a large-scale development of TDD-LTE (time division duplex long-term evolution) commercial network, in some countries or regions, there will be cases where multiple operators deploy TDD-LTE networks in a same geographical area, and it can be foreseen that such cases will become more prevalent. Currently, there are cases that multiple operators operate the TDD-LTE network at adjacent channels in the frequency bands of both 2.6 GHz and 2.3 GHz in China, and no guard band is reserved between frequency bands owned by the operators.
In a case that multiple operators deploy TDD networks in adjacent frequency bands in a same geographical area, severe interference will be caused if synchronization and coordination of uplink/downlink time slot allocation are not performed between the operators. For example, if a base station (a terminal) of an operator is in a transmit mode, and a base station (a terminal) of another operator is in a receive mode at a same time instant, a receiver may have a ground noise rising or even be blocked due to out-of-band radiation characteristics of a transmitter and undesirable adjacent channel selectivity of the receiver, thereby affecting the reception of useful signal by the receiver. In this case, it is necessary to provide a guard band and/or an additional radio frequency filter and/or other interference cancellation to reduce the interference.
In addition to providing the guard band and the additional filter to avoid the interference, another method is to negotiate by the multiple operators for synchronous operation between the TDD systems. That is, base stations of the TDD systems of multiple operators are all in a transmit state or a receive state in a same time instant.
Considering in view of spectrum utilization and an extra renovation cost of a device, synchronization between TDD systems is the most effective scheme of deploying the TDD systems in a same geographical area in adjacent frequency bands by multiple operators. Hence, an operable and effective solution of synchronization between multiple operators is crucial for ensuring a stable and reliable operation of TD-LTE systems.
Regarding the synchronization between TDD systems of multiple operators, various operators have a common point that, it is desirable to have a reliable and credible scheme for finding and proving a base station or a cell which is out of step. It is proposed to find and prove the out-of-step base station with a scheme of detecting an interference source on the base-station side and analyzing an interference model. However, the scheme can only prove that there is no perfect synchronization between base stations, but has great difficulties in proving which base station is out of step. Currently, the operators and manufacturers generally believe that a test made by a third party have a higher credibility.